What's this problem talking about?

  • Thread starter Thread starter AznBoi
  • Start date Start date
AI Thread Summary
The problem discusses the energy efficiency of transportation methods, specifically comparing bicycling and walking to automobile travel. It highlights the energy expenditure of a cyclist at 400 kcal/h and a walker at 220 kcal/h, emphasizing the need to convert these values into joules per gallon for comparison with gasoline's energy yield. The conversion process involves understanding that 1 kcal equals 4,186 J and that gasoline provides approximately 1.30 x 10^8 J/gal. The discussion concludes with a user successfully solving the problem through continuous conversions. This illustrates the importance of careful reading and methodical calculation in solving energy-related problems.
AznBoi
Messages
470
Reaction score
0
I've come across a problem and I have no idea on how to solve it.. I know it involves converting units but how do you convert kcal/h into J/gal? Please take your time to help me get started. Thanks!

Here is the problem:
For saving energy, bicycling and walking are far more efficient means of transportation than is travel by automobile. For example, when riding at 10 mi/h, a cyclist uses food energy at a rate of about 400kcal/h above what he would use if merely sitting still. (In exercise physiology, power is often measured in kcal/h rather than in watts. Here 1 kcal=1 nutritionist's Calorie = 4,186 J) Walking at 3mi/h requires about 220 kcal/h. It is interesting to compare these values with the nergy consumption required for travel by car. Gasoline yields about 1.30 x 10^8 J/gal. Find the fuel economy in equivalent miles per gallon for a pesron a) walking, and b) bycicling.
 
Physics news on Phys.org
It's all right there in the problem. Just read it a bit more carefully, starting with the fuel economy for walking.
 
Yeah I figured it out. I just kept converting and converting lol until I ended up with mi/gal. k thanks
 
I multiplied the values first without the error limit. Got 19.38. rounded it off to 2 significant figures since the given data has 2 significant figures. So = 19. For error I used the above formula. It comes out about 1.48. Now my question is. Should I write the answer as 19±1.5 (rounding 1.48 to 2 significant figures) OR should I write it as 19±1. So in short, should the error have same number of significant figures as the mean value or should it have the same number of decimal places as...
Thread 'Collision of a bullet on a rod-string system: query'
In this question, I have a question. I am NOT trying to solve it, but it is just a conceptual question. Consider the point on the rod, which connects the string and the rod. My question: just before and after the collision, is ANGULAR momentum CONSERVED about this point? Lets call the point which connects the string and rod as P. Why am I asking this? : it is clear from the scenario that the point of concern, which connects the string and the rod, moves in a circular path due to the string...
Thread 'A cylinder connected to a hanging mass'
Let's declare that for the cylinder, mass = M = 10 kg Radius = R = 4 m For the wall and the floor, Friction coeff = ##\mu## = 0.5 For the hanging mass, mass = m = 11 kg First, we divide the force according to their respective plane (x and y thing, correct me if I'm wrong) and according to which, cylinder or the hanging mass, they're working on. Force on the hanging mass $$mg - T = ma$$ Force(Cylinder) on y $$N_f + f_w - Mg = 0$$ Force(Cylinder) on x $$T + f_f - N_w = Ma$$ There's also...
Back
Top